Don't worry, a lot of us have also gone through this too. I've had my fair share of rank-downs from S that I've had to work back up to (in fact, I'm in the middle of one now...), and I guarantee you that you are not alone. I know it gets frustrating, but that's all part of learning more about the game and how to improve. Just keep practicing to work back up to S-rank. You can do it!
With that being said however, if you find yourself on tilt, take a break from the game! I know it's hard to resist the urge to keep going and redeem yourself, but tilts don't help with improving. They just make us more frustrated and play worse. Trust me, I've learned from experience and it's not a pretty sight. It's good to get your mind off of it and reflect/recharge so that you're ready to jump back in (hopefully with your skill at its peak condition) with more energy and less salt.
It's understandable for rank-downs and tilting to feel daunting, but don't let it discourage you. You can always earn your S back; you'll only get better as you keep playing and improving. I believe in you! :3